Rejetting required with UFO exhaust?

[Traumahawk]

I think I will only change the main jets for now. Leave the needles as it has been. Bought the bike last year, beeing an 85 I bet someone have had an aftermarked exhaust on it before. So just change mains to 150 and test how the bike reacts to the UFO. Drive aroud for a day or so and then start testing different clips on the needles.

Thats the best way to tune. On the Vmax, you tune from the top down. You get the main jet right, then work on the needles, the mess with the A/F screws

 

[Traumahawk]

I was just looking thru my Vmax file, and I found a pic that might help explain how and where to shim the needles........if you need to.

 

[NorwegianMAX]

I was just looking thru my Vmax file, and I found a pic that might help explain how and where to shim the needles........if you need to.

Thats a great photo! Thanks. Ill by this shim kit if I end up with best performance between, for instance, between slot 3 or 4 from blunt end.

 

[blaxmax]

Thats a great photo! Thanks. Ill by this shim kit if I end up with best performance between, for instance, between slot 3 or 4 from blunt end.

You have have a 1/2 step washer stored on top of your "c" clip on each needle.

 

[NorwegianMAX]

The spare carbs had 175 mains in them. In the the Dynojet stage 7 instruction manuel I found online thy say to install DJ165 mains if you have stock modified exhaust and DJ175 mains for aftermarked exhaust. Is the DJ175 the same as the 150 main jets you refer to?

 

[Traumahawk]

No, they arent. Dynojet has their own numbering system. Let me post up a comparison. The DJ 175's are between the mikuni (MK) 162's and 165's. Stock is Mk 152's. Dynojet has you set up the carbs pig rich.

I looked thru some old copies of Vboost, at some of the early dynos. There were stage 7 bikes, that posted HP numbers down in the 90's. Stock Vmax's were in the 105-115 range.

DJ160 is equal to a MK 150.

Maybe this will put it into perspective. Here is a comparison dyno run from last fall between 150's and 155's mikuni. So best hp for my bike is 119, so far, I am running a heavy RC wheel, and so loosing probably 4 hp, so that way you can compare with other bikes using stock wheels. So, with a stock wheel, I would be 122-123 ish, which is what you can expect with a jet kit, and aftermarket exhaust.

 

[maleko89]

Mikuni numbers are based on the size of the outlet. DJ jets by flow rate...I believe.

Mark

 

[yellowmax94]

Like Tramahawlk said they are loud. I would recommend changing the mains. Your elevation will also make a big difference. I would even recommend dropping down to the 147.5s.. I love my UFO's, as long as I have my ear plugs in... Most other people hate riding near me..

Hi, I have a '94 that is 100% stock internally and I added a UFO 4-1 Dragstar (LOUD) exhaust. I just swapped out the main jets to 147.5's and it did really clean it up. Did you make any other jetting changes? I realize you have the Muscle Kit so we're not really comparing apples to apples, just curious?

I still have a little sputter at times when running at slow speeds (behind farm machinery, for example!). When I accelerate around them it will hesitate. scary... was wondering if there is something else i need to adjust? Btw, that was the first time that i ever took the carbs off myself and i've had the bike for 22 years, lol. I am NOT a mechanic

 

[blaxmax]

Hi, I have a '94 that is 100% stock internally and I added a UFO 4-1 Dragstar (LOUD) exhaust. I just swapped out the main jets to 147.5's and it did really clean it up. Did you make any other jetting changes? I realize you have the Muscle Kit so we're not really comparing apples to apples, just curious?

I still have a little sputter at times when running at slow speeds (behind farm machinery, for example!). When I accelerate around them it will hesitate. scary... was wondering if there is something else i need to adjust? Btw, that was the first time that i ever took the carbs off myself and i've had the bike for 22 years, lol. I am NOT a mechanic

You are now-- try turning your a/f mixture screws out maybe 1/2 turn.

 

[Traumahawk]

Hi, I have a '94 that is 100% stock internally and I added a UFO 4-1 Dragstar (LOUD) exhaust. I just swapped out the main jets to 147.5's and it did really clean it up. Did you make any other jetting changes? I realize you have the Muscle Kit so we're not really comparing apples to apples, just curious?

I still have a little sputter at times when running at slow speeds (behind farm machinery, for example!). When I accelerate around them it will hesitate. scary... was wondering if there is something else i need to adjust? Btw, that was the first time that i ever took the carbs off myself and i've had the bike for 22 years, lol. I am NOT a mechanic

What rpm are you at when your at slow speeds? If your 3000-4000, thats where the needles start kicking in, so you might need to shim the needle. If its lower rpms, then turn out the A/F screws 1/2 -1 turn out depending on where your starting from.

 

[DMAN999]

Like they said it depends on what rpm/throttle position gives you a stumble.
The picture below shows what parts of our carbs are affected at different throttle positions.

 

[yellowmax94]

What rpm are you at when your at slow speeds? If your 3000-4000, thats where the needles start kicking in, so you might need to shim the needle. If its lower rpms, then turn out the A/F screws 1/2 -1 turn out depending on where your starting from.

Thanks, it is around 2000 I believe. I'm sure it's under 3000. I'm learning all kinds of things here. Thanks.

Sent from my SAMSUNG-SM-G920A using Tapatalk

 

[sdt354]

Check the float levels before taking the carbs off. Then adjust if need be while the bowls are off anyway. Let us know if you need pics or help. Fuel level is critical to a good tune. More so than I ever expected. You can make decent HP with some tuning. And get better milage. I did something with my air box I always wantesd to try. I took the Y off and opened the lid up to match the K&N filter. I had the stage 7 kit installed already. The 165 DJ's could be down sized with this set-up. The torque is great on the bottom end with this set up. The stage 7 springs made my throttle real twitchy. Like lunge at a slight twist. I found some in between stock and stage 7 that worked well for regular riding. They may have been Venture's. I might go withy the 7 springs again just to see how it works with this set-up.
Steve

 

[NorwegianMAX]

A small update.
I have now installed the UFO 4-2-2 exhaust. Shiiiiiiitttt THOSE are loud as f***!!! Even with the smaller endcaps.
Tried the bike out for a week without adjusting anything. Crazy fun
The super weird thing is that the consumption went from 24 mpg to 42 mpg! I have changed the cracked rubber tubes between airbox and carbs this winter so this might help also.
The bike still pulls quite strong, but maybe a bit less top end pull. So i will change the mains to 150.
But when cruising without loading the engine, the exhaust is popping and sputtering.. This means too rich og to lean? og maybe a carb sync is needed? Or needle adjustment og neddles need to be moved one clip further in?
The bikes is very responsive now, with a bit more low end power i think.. No problem rolling burnout 1. 2. and 3. gear... This ****** 10 years old rear tire is garbage need somethink more sticky like ME880 or Shinko.
Thanks guys.

 

[Traumahawk]

At what RPM is it popping and sputtering?

 

[NorwegianMAX]

maybe 2000-5000rpm. Not sure really, feels like it is popping at all rpms when Im not pushing the engine. If I accelerate it runs very well. Therefore I am thinking maybe a carb sync is needed?

 

[Traumahawk]

If the carbs have not been sync'd by you....then yes, that will help. If you can, next time just look at what the RPMs are when your having issues, and that will denote what part of the carb gets tuned.

Dont forget that you tune a Vmax from the top down. So, you first put in the proper main jets, then get the needles set correctly, then the A/F screws.

You can completely tune the carbs without know the float level, but knowing the float level is what you will need to maximum hp, if your going for that.

 

[asherc]

A small update.
I have now installed the UFO 4-2-2 exhaust. Shiiiiiiitttt THOSE are loud as f***!!! Even with the smaller endcaps.
Tried the bike out for a week without adjusting anything. Crazy fun
The super weird thing is that the consumption went from 24 mpg to 42 mpg! I have changed the cracked rubber tubes between airbox and carbs this winter so this might help also.
The bike still pulls quite strong, but maybe a bit less top end pull. So i will change the mains to 150.
But when cruising without loading the engine, the exhaust is popping and sputtering.. This means too rich og to lean? og maybe a carb sync is needed? Or needle adjustment og neddles need to be moved one clip further in?
The bikes is very responsive now, with a bit more low end power i think.. No problem rolling burnout 1. 2. and 3. gear... This ****** 10 years old rear tire is garbage need somethink more sticky like ME880 or Shinko.
Thanks guys.

?

 

[blaxmax]

maybe 2000-5000rpm. Not sure really, feels like it is popping at all rpms when Im not pushing the engine. If I accelerate it runs very well. Therefore I am thinking maybe a carb sync is needed?

Check your spark plugs after running around a day or so not pushing it-(white would be lean) sounds like your a/f screws need turning out more. Some guys are using cops and getting rid of that sputter with a different spark. You can read about them here----- http://www.vmaxforum.net/showthread.php?t=40699